If you are going to keep him (I'm not sure of the legalities of that ) make sure you put some hiding places for him in the tank. Don't forget, they are ambush predators so they need to be able to hide to feel safe and secure. Also, be glad it's not a small Musky. You'd need a really big tank to keep it in then lol
No! I'd never keep something this big and it's illegal like you said, catch and release( after watching him for a bit!)